In automatic transmissions, a driver can activate the corresponding program via an E/S/W (economy/sport/winter) w push-button. In automatic transmissions, having a so-called "intelligent switching program", the selection of the switching point or the step of the winter program is automatic. A process for activating the winter program has been disclosed, e.g., in ATZ Automobiltechnische Zeitschrift 94 (1992), page 432. It is proposed that unauthorized slip be detected from the comparison of driven and non-driven gears. Depending on the result of said examination, a slip index is set. The winter program is activated when within a fixed preset time period, the sum of these values exceeds a preset limit value. In the practice of the process described, there can arise the problem of reaction time lapses. Reaction time lapses are a result of fixed slip index values, which create long periods between the occurrence of the slip and the activation of the winter program.
In view of the above, the problem to be solved by the invention is for the invention to quickly adapt the performance characteristics of the automatic transmission to the outerwinter operation driving conditions. The invention solves the problem by the fact that a driving state is set at a low friction value when either an ABS deceleration or a slip is detected.
If an ABS deceleration state signal is received by the ABS control unit of the electronic transmission control, a meter determines, via an ABS evaluation function, the actual acceleration of the vehicle or a parameter corresponding to an actual acceleration (e.g., gear speed increase). The ABS evaluation function is carried out so that with each value of the actual acceleration of the vehicle, a meter offset will be coordinated via a characteristic line. The meter count results from the actual meter count plus the offset. If the meter count exceeds a limit value, an electronic transmission control activates the winter operation.
In the case of a slip, the meter will make its determination by means of a slip evaluation function from the theoretical/actual comparison of the vehicle acceleration or a parameter corresponding to the theoretical/actual comparison of the vehicle acceleration (e.g. torque reserve). The slip evaluation function is carried out so that with each value of the theoretical/actual comparison of the vehicle acceleration, a meter offset is coordinated via a characteristic line. If the meter count exceeds a limit value, an electronic transmission control activates the winter operation.